The field of the present invention is the structural and suspension architecture of motorcycles.
Conventional motorcycles comprise a separate frame structure including head pipes, main pipes, down tubes and the like. Such a frame is the basic structure for the motorcycle for supporting the power unit, the front suspension and the rear suspension, among other things. The frame receives reaction forces from the front and rear wheels and serves to suspend the body of the motorcycle and the mechanisms mounted thereon. The requirements for such a frame are, therefore, substantial and the frame is typically a heavy component of the vehicle.
Motorcycles have been developed which eliminate the heavy frame. One such motorcycle is illustrated in Japanese Patent Publication No. 58-49435. The motorcycle of that publication employs connecting plates fixed to a power unit. A front swing arm assembly is then mounted to the mounting plates. The assembly in turn supports a front wheel. In a similar manner, a rear fork assembly is pivotally mounted by plates also fixed to the engine and in turn mounting a rear wheel. In this mechanism, the engine serves as the body frame for sustaining static and dynamic loads of the front and rear suspension assemblies. Such vehicles are found to be of reduced weight and lowered center of gravity. Another vehicle also understood to eliminate at least portions of the frame is illustrated in Japanese Patent Publication No. 53-142739.
With the foregoing vehicles, the shape and strength of the power unit becomes important for considerations other than proper power unit design. The additional mounting brackets also contribute weight to the overall vehicle.